In pulp mills, it is necessary to be able to sluice chips or other lignocellulose material, as well as cooking liquids or other treatment fluids, between lines or vessels which have different pressures. Thus, chips are sluiced via a so-called low-pressure feeder into a steaming vessel where a certain steam pressure is maintained, for example about 150 to 200 kPa. After the steaming, the chips and cooking liquid are sluiced via a high-pressure feeder into the high-pressure system of the digester, in which system a considerably higher pressure is maintained. A high-pressure feeder -- i.e. a sluice charger intended to be able to operate at high pressure differences -- of a conventional type is shown in FIG. 1 and FIG. 2. It consists of a charger housing 1 and a rotor or so-called feeder 2. The latter is divided into a number of compartments 3 for sluicing chips via an inlet opening 4 and cooking liquid through an inlet opening 5 to the pulp digester via an outlet opening 6. The shaft of the feeder is designated by 7. The feeder 2 has the general shape of a truncated cone, the circumferential surface of which is designated by 8. The latter is pressed against a correspondingly shaped surface 9 in the charger housing 1. As a result of the friction between the surfaces 8 and 9 upon rotation of the feeder 2 (the members for executing this rotation are not shown in the figures), the surfaces 8 and 9 become worn. The setting of the feeder 2 therefore has to be gradually adjusted by means of its being displaced axially relative to the charger housing 1. For decades now, various screw arrangements in adjustment apparatuses connected to one end of the feeder shaft 7 have been used for this adjustment. A common feature of these apparatuses is that they required relatively great force for manoeuvring them, and at the same time they provided only limited adjustment precision in many cases. Systems have also been developed for automatically regulating the position of the feeder. For example, Swedish published patent application 9300219-4 describes such an arrangement, but it does not touch upon the abovementioned problems.